Ignition coils provide high voltage impulses to spark plugs of internal combustion engines. Conventional internal combustion engines utilize a distributor and single ignition coil to provide high voltage impulses to spark plugs in sequence determined by the distributor. The distributor included a mechanical rotor and a contact associated with each spark plug.
To meet fuel economy standards, exhaust emission standards and to extend maintenance intervals distributorless engine ignition systems have been developed. Distributorless systems have no moving parts which require replacement or adjustment. Instead, an electronic digital timing circuit sequences the impulses for engine spark plugs.
Twin tower ignition coils have been developed to allow two spark plugs to operate from one ignition coil. Positive and negative pulses from opposite ends of the coil fire on each input from the electronic timing circuit. In this arrangement, a spark is supplied via one tower to a spark plug when its associated cylinder is in the compression stroke and simultaneously provides a spark via the other tower to a spark plug with an associated cylinder in its exhaust stroke. An example of such a system is disclosed in U.S. Pat. No. 4,763,094 to Kojina which describes an ignition coil assembly for an internal combustion engine with four cylinders.
According to the Kojina patent the ignition coil assembly includes first and second primary and secondary coils embedded in a housing. The ignition coil assembly disclosed in Kojina is a bulky assembly. Electrical connections between the various coils and connector terminals require soldering at multiple points. Air gap tolerances and visual injection molding processes allow water entry into internal flux paths. The tolerance variability associated with manufacture of the steel core laminations (a stamping operation) complicates the injection molding process, which typically requires high-precision inserts. In addition, a small tolerance is necessary to establish an effective air gap in the magnetic flux path between the "C" lamination and laminated core embedded in the primary bobbin. These two effects taken together magnify variability in the production process and make insert molding of the laminations very difficult. The prior art (Kojina) could not address this variability and chose a more costly and complicated solution: the addition of two-layer mylar tape into the air gap described.
As a result of the above compromise employed by Kojina in the prior art, openings exist from the exterior of the housing to the encapsulated interior lamination. These can degrade over time causing an electrical "short" from the laminated core to the primary winding.
The ignition coil assembly disclosed in Kojina is a dedicated design intended only for use with a four cylinder engine. Use of such a coil assembly design would be inappropriate for a two cylinder engine. Four, six and eight cylinder engines would each require different assembly lines, additional tools and injection molds. Production costs are also adversely impacted by increasing the number of parts required to make different ignition coil assemblies for each engine.